Well, I don't know more on this that you do, but 5.1 near El Centro is interesting; maybe worrying. We still don't have a focal mechanism. The crust may be thin in this area so to get a M6.9 it may have to rupture a long distance, if it is strike-slip. So, could it have ruptured all the way up to and across the border? It would have probably had to jump between or across mapped fault segments. Not impossible (Landers 1992). Time will tell.
Chris